X-ray tue components Flashcards
what does the x-ray tube insert provide
it provides a source of electrons free to move
it allows electrons to travel accross the x-ray tube at high speeds
allows the elctrons the change direction to the target of the anode
what is an x-ray tube insert
it is made out of heat resistant glass and it holds all the components of the anode and cathode.
it is also tightly sealed in order to maintain the vaccum inside it allowing the electrons from the cathode foilament to flow freely
what is the issue with the tube insert being made out of glass
the glass can become gassy from tungsden vapour from the filament and the anode
this form a thing layer of gas inside the insert which can conduct electricity and puncture the glass
what is the cathode of an x-ray tube
this is the negative end of the x-ray tube
it consists of the filament, focussing cup, filament supply and the high tension supply to the negative end of the x-ray tube circuit
what is the filament
the filament provides a source for electrons required for x-rays
the filament is made of a thin piece of tungsden wire made into a coil which provides a larger surface area for electron emissions wile taking up less space
what properties make tungsten suitable for use in filaments
strong and ductile
high melting point
low vapour pressure so less atoms are lost from the filament surface
a good thermionic emitter meaning it readily releases electrons heated
low work function
what are the 2 focuses of an xray tube
broad and fine focus
what is the function of broad focus
the broad focus is the larger filament and it is used when imaging larger body parts like the spine where a larger surface area is covered and more radiation is required.
the images when on the broad focus setting are less sharp
what is the function of fine focus
fine focus filqament is used ti image smaller body parts like the hand where a sm,aller surface area is covered and less radiation is required
these images do appear sharper but a low tube current must be used
what is the focussing cup
the focussing cup houses the broad and fine focus and is a depression in the filament
it has a high melting point to withstand high temperature but it is a poor thermionic emitter
the function is to direct electron emition from the filament directly to the focal track of the anode. its sharp edges also are negatively charges when voltage is applied meaning electrons are repelled directly towards the anode
what does the anode side of an xray tube consist of
the anode disc
the anode stem
rotor
high tension connection for the anode side of the tube circuit
describe the composition of the anode disc
the focal track made of a rhenium and tungsten alloy
the tungsten is crucial in this disc as it has a low vapour pressure, high melting point and it also has a high atomic number meaning it has a great positive charge
the rhenium is important for preventing wear and tear of the focal track as it converts the filament electrons into x-ray energy
the graphite helps to reduce the overal mass of the disc increasing thermal capacity
what is the purpose of the anode disc
the anode disc bevelled edges are what form the focal track and the larger the disc , the ;arger the focal track
the rotation of the disc helps heat to spread over a larger surface area
what is the rotor
the rotor is a hollow cylinder that helps to support the stem
it is made out of copper due to its high conductivity of both heat and electricity
the rotation occurs when alternating voltages are applied across the stator windings
